A rotary loop taker is a device that must be incorporated into all lock-stitch sewing machines. Perhaps 70 to 80 per cent or more of all industrial sewing machines are of the lock-stitch type, and therefore utilize a rotary loop taker. Lock-stitch sewing machines of the type described are especially useful for sewing canvas, leather, or other heavy materials.
The conventional loop taker is precision machined of fine steel to accurate proportions and balance throughout its extent from its weighted hub to its fragile hook or "loop seizing point." It is a costly item, and a short-lived item under the heavy wear and tear that accompanies the use of a typical industrial sewing machine. Conventional loop takers have a life of only three to six months, depending on the many variables involved.
The most vulnerable part of the fragile loop seizing point of a rotary loop taker is the tip. The tip can, for example, be chipped by the needle of the sewing machine, or burred by the friction that is created by the high speed revolutions of the loop taker as it picks up the thread off the needle. Since a faulty hook or loop seizing point tends to skip stitches, it must be repaired or replaced whenever the fragile loop seizing point accidentally breaks or becomes too dull through normal wear.
With a rotary loop taker of the conventional type, most factories simply discard the entire device when the loop seizing point (which is conventionally an integrally formed part of the loop taker) becomes chipped or otherwise rendered unusable. Others send the rotary loop taker to a facility that reprocesses the tip of the loop seizing point at great time loss. Either expedient is very costly.
Loop takers of the conventional type are customarily provided with a circular raceway around the inner wall to accept a bearing rib located on the exterior of the bobbin case. It has long been recognized that with use this raceway invariably becomes flawed--especially in the initial portion of the raceway, which is the most vulnerable to damage--and in this condition restricts the free passage of the thread around the bobbin case. As a consequence of such damage to the raceway and resulting restriction of free passage of the thread, thread breakages frequently result.
Another troublesome condition that results from the wearing of the bobbin case raceway in the conventional rotary loop taker is known in the industry as "slop." This condition is the excessive "play" between the bobbin case and the inner wall of the loop taker which defines the bobbin case raceway.
"Slop" interferes with the proper release of the top thread (i.e., the needle thread) from around the bobbin case, and increases the incidence of jamming between bobbin case and raceway. It also tends to cause large, undesirable loops of top thread to be formed on the bottom of the material being sewn, because of the premature closing of the escape exit for the top thread. It may also cause the top thread to break, if a bunching of thread occurs because of the degree of "slop" that is present. Finally, if the "slop" is great enough to produce serious jamming of the top thread, the upper ledge of the bobbin case raceway on the loop seizing point may be broken as the operator manipulates the bobbin case in an attempt to free up the jammed thread.
When the raceway of a rotary loop taker of conventional construction becomes damaged in any manner just described, the entire rotary loop taker must be totally replaced.
The rotary loop taker covered by applicant's above mentioned application Ser. No. 355,228 overcomes the disadvantages of the prior art just discussed. The loop taker of the present invention has the basic advantages of the rotary loop taker covered by that application, and provides additional important advantages as well.